Large towers still kill plenty of pilots.

Keep in mind the biggest tower in the world is only 1600' above ground, or 1900' above sea level. It is also fixed in place and very visible. I can see it from my house, 30km away :-)

If you put a floating power station on a 20,000' tether, it's going to move around quite a lot, over a very large area, and be completely invisible to pilots. Airspace restrictions don't really work in this case. They work when they cover large highly visible areas like military installations, not pinpoint, completely invisible stations.

You might get better bang for the buck mounting a 1,000' tether at the top of a high mountain, as long as there is a populated area nearby to use the power.